This invention relates to a squish structure for a spark ignition engine and more particularly to an improved combustion chamber configuration for an internal combustion engine.
The use of combustion chambers having squish action in internal combustion engines are well known. With such combustion chambers, the piston, cylinder bore and cylinder head define a relatively large combustion chamber volume at top dead center position of the piston. Along at least one side of this combustion chamber volume there is defined a relatively narrow squish area. As the piston approaches top dead center, the charge which is compressed in the squish area is driven at a high velocity into the larger combustion chamber area to create turbulence and improve flame propagation.
Although such squish type combustion chambers do promote turbulence and improve some running characteristics of the engine, the squish volume itself forms an area which gives rise to incomplete combustion. That is, although the squish area is effective for creating turbulence in the main combustion chamber volume, the rapid flame propagation in the main combustion chamber volume cannot propagate into the restricted squish area and as result any fuel in the squish area will not be completely burnt during running. This obviously gives rise to poor fuel economy and high exhaust gas emissions.
In addition to this problem, the squish area is generally cooled more than the remainder of the combustion chamber because of its actual configuration and the fact that is has a smaller volume to surface area than the main combustion chamber. As a result, a quenching action occurs in the squish area which further deteriorates the combustion in this area. In addition, the delayed combustion caused by the squish area can give rise to problems in knocking or pre-ignition.
An arrangement has been proposed where a pre-chamber communicates with the squish area through a restricted throat. The purpose of this concept is to cause combustion to occur in this small chamber and this flame is then suppose to propagate into the squish area through the restricted throat. Although this concept appears feasible, the fact that there is a restricted throat that communicates the squish area with the small pre-chamber gives rise to significant pumping losses and, therefore, the system does not work as planned. In addition, the small throat area causes throttling of the burning charge which issues from the pre-chamber and this causes heat loss which further diminishes the efficiency of such arrangements.
It is, therefore, a principal object to this invention to provide an improved combustion chamber configuration for an internal combustion engine.
It is a further object to this invention to provide an improved combustion chamber configuration that embodies a squish area for creating turbulence in the main combustion chamber volume but which also incorporates an arrangement for insuring complete combustion of the charge in the squish area without throttling and pumping losses.
Even if a small pre-chamber communicates in an unrestricted fashion with the squish area to promote combustion in the squish area, there may be times when combustion cannot or will not be initiated in the small pre-chamber.
It is, therefore a still further object to this invention to provide an improved combustion chamber configuration including a squish area at a pre-chamber and wherein it is insured that combustion will always be initiated in the pre-chamber.